The present invention is related to a linear actuator.
Japanese Laid-Open Patent Publication No. HEI 7-184382 discloses a mechanism in which a slider is movably provided with respect to a shaft, and an AC voltage is applied to a piezoelectric element of a vibrating element (micromotor) to vibrate the vibrating element, whereby such vibration applies force to the slider to move the slider along the shaft.
However, in this mechanism, because frictional driving is carried out by pushing force applied to the slider from the vibrating element, the frictional resistance between the slider and the shaft increases and there are large losses depending on such pushing force, and there are cases where the slider can not move because the frictional resistance is too large.
It is an object of the present invention to provide a linear actuator having a simple structure which has the advantage of being compact, and particularly thin, and which makes it possible to smoothly and reliably move a slider.
In order to achieve the above-mentioned object, a linear actuator of the present invention has at least one actuator unit. The actuator unit comprising: a slider; a plurality of rollers for movably supporting the slider; and a vibrating element abutting on the slider to make frictional contact with the slider, the vibrating element having at least one piezoelectric element; wherein the vibrating element is vibrated when an AC voltage is applied to the at least one piezoelectric element so that the vibration repeatedly applies force to the slider to move the slider lineally.
Thus, it is possible to reduce the frictional resistance, and this makes it possible to linearly move the slider smoothly and reliably. Further, by using a vibrating element to move the slider, namely, by using a vibrating element to linearly drive the slider, the entire linear actuator can be made compact and particularly thin. Also, the structure of the linear actuator can be simplified, and this makes it possible to reduce the manufacturing cost. Further, because an ordinary motor is not used, it is possible to completely eliminate electromagnetic noise, or even when there is electromagnetic noise, because such noise is small, it is possible to prevent such noise from having an effect on its peripheral devices.
In the linear actuator of the present invention, it is preferred that the at least one actuator unit includes a plurality of actuator units.
In the linear actuator of the present invention, it is preferred that the plurality of actuator units are respectively provided in substantially parallel planes in a stacked arrangement.
In the linear actuator of the present invention, it is preferred that the linear actuator further comprises: at least one common shaft for rotatably supporting the rollers of the actuator units; and at least one common shaft for supporting the vibrating elements of the actuator units.
In the linear actuator of the present invention, it is preferred that the vibrating element has vibrating patterns which comprise a plurality of vibrating modes including a first mode in which the slider is maintained in a suspended state; a second mode in which the slider is allowed to be moved; a third mode in which the slider is moved in a forward direction; and a fourth mode in which the slider is moved in a reverse direction, wherein any one mode can be selected from the first mode, the second mode, the third mode, and the fourth mode by changing the vibrating pattern of the vibrating element.
In the linear actuator of the present invention, it is preferred that the vibrating element has vibrating patterns which comprise a plurality of vibrating modes including a first mode in which the slider is maintained in a suspended state; a second mode in which the slider is allowed to be moved; a third mode in which the slider is moved in a forward direction; and a fourth mode in which the slider is moved in a reverse direction, and the vibrating element has a plurality of divided electrodes so that the vibrating element is vibrated when an AC voltage is applied to the at least one piezoelectric element through the electrodes, wherein any one mode can be selected from the first mode, the second mode, the third mode, and the fourth mode by changing patterns of application of the AC voltage to each of the electrodes of the vibrating element.
In the linear actuator of the present invention, it is preferred that the linear actuator further comprises at least one shaft positioned at the center of the corresponding roller for rotatably supporting the roller, wherein the slider is positioned in the groove to be supported by the roller, and the diameter of the shaft is smaller than a portion of the roller on which the slider is supported.
In the linear actuator of the present invention, it is preferred that the slider has a sliding portion and the sliding portion is rod-shaped or plate-shaped.
In the linear actuator of the present invention, it is preferred that the vibrating element is plate-shaped, and the vibrating element and the slider are positioned in a substantially same plane.
In the linear actuator of the present invention, it is preferred that the vibrating element is constituted from a laminated body which includes the at least one plate-shaped piezoelectric element and at least one reinforcing plate made of metal material.
In the linear actuator of the present invention, it is preferred that the vibrating element has an arm portion projectingly provided from the vibrating element to support the vibrating element, the vibrating element is pushed into contact with the slider by the arm portion, the vibrating element has a portion abutting on the slider, and the arm portion and the abutting portion are formed integrally on the reinforcing plate.
In the linear actuator of the present invention, it is preferred that the linear actuator further comprises pushing means for pushing the vibrating element into contact with the slider; wherein the vibrating element has an arm portion projectingly provided from the vibrating element to support the vibrating element, the vibrating element has a portion abutting on the slider, and at least a part of the pushing means, the arm portion, and the abutting portion are formed integrally on the reinforcing plate.
In the linear actuator of the present invention, it is preferred that the pushing means has an adjustment mechanism that adjusts force pushing the vibrating element against the slider, and at least a part of the adjustment mechanism is formed integrally on the reinforcing plate.
In the linear actuator of the present invention, it is preferred that the vibrating element has a portion abutting on the slider, the abutting portion is positioned between two rollers of the plurality of rollers in a direction of movement of the slider.
In the linear actuator of the present invention, it is preferred that the slider has a resonance frequency of bending vibration, and the linear actuator is constructed so that there is substantially no match between the resonance frequency of the bending vibration of the slider and the m""th multiple of the frequency of the vibration of the vibrating element (where m is all of the natural numbers), and that there is substantially no match between the n""th multiple of the resonance frequency of the bending vibration of the slider and the frequency of the vibration of the vibrating element (where n is all of the natural numbers).
In the linear actuator of the present invention, it is preferred that the linear actuator further comprises movement restricting means for restricting movement of the slider.
In the linear actuator of the present invention, it is preferred that the movement restricting means is provided on the slider, and includes at least one protruding portion that restricts the movement of the slider by abutting on the roller.